This invention relates to MESFET logic which includes voltage level shift circuits.
MESFET (metal-semiconductor field effect transistor) technology is becoming of importance both for Si (silicon) and GaAs (gallium arsenide) technology. GaAs digital electronics uses mainly depletion mode MESFET technology. In typical circuits negative voltage logic input signals are required while the output voltage is positive. To connect gates, level shifters are needed to shift the positive voltage output signals such that they become suitable for the input to the next gate. Commonly, a string of Schottky diodes in connection with a current source is used for this level shifting function. The level shifting circuit uses GaAs surface area, consumes power, requires often a separate power supply and adds to the delay of the circuit.
Capacitors have been used for level shifting for many years, and were even commonly used in tube type amplifiers. For example, U.S. Pat. No. 4,035,662 discloses a circuit which uses capacitors for shifting voltage levels in insulated gate field-effect-transistor inverter-type circuits. U.S. Pat. No. 4,109,163 is for a high speed radiation hard complimentary MOS capacitive voltage level shift circuit. IBM Bulletin Vol. 17, No. 5, October 1974, shows a circuit for capacitively stabilizing a substrate voltage. IBM Bulletin, Vol. 21, No. 2, July 1978, discloses a circuit which includes capacitors for shifting voltage levels. However, it should be noted that each type of semiconductor technology presents its own problems requiring solution.